in September after she was dropped from the procedural over the summer for "creative reasons." She returned last month to reprise her role as agent and media liaison Jennifer "JJ" Jareau for Paget Brewster's final episode.

Brewster, who was demoted this season before deciding to leave the show, could also return as a regular next year, as CBS has an option on her contract. She recently joined the NBC pilot My Life As an Experiment and would stick with it if it goes to series.If Cook and/or Brewster return — as many fans have been hoping for since the cast upheaval — it is unclear what that will mean for Rachel Nichols, who was promoted to series regular in December.

The cast shake-up may not end there: Thomas Gibson and Shemar Moore are currently not signed for next season. Negotiations for both are under way.Meanwhile, Bernero informed the cast Tuesday night of his departure. Bernero — who became showrunner when creator Jeff Davis left after the first season and steered the show into a solid hit for CBS — had already stepped aside this season to run the spin-off, Criminal Minds: Suspect Behavior. He also has a pilot, Partners, at ABC.

Longtime executive producer Erica Messer will take over as showrunner. Messer and fellow executive producer Simon Mirren, who is also leaving this season, had been acting showrunners this year.CBS had no comment.